Process for treating mixtures of oxy salts of arsenic, antimony, and tin



Pas a Apr. 22, 1930 UNITED STATES PATENT OFFICE HELVILLE FLETCHER PERKINS, OF TACOMA, WASHINGTON, AND CHARLES W. HAN SON, OF PERTH AMBOY, AND BERRY MARVEL OHARRA, F WESTFIELD, NEW JERSEY, ASSIGNORS TO AMERICAN SMELTING AND REFINING COMPANY, 01' NEW YORK, N. Y., A CORPORATION OF NEW JERSEY PROCESS FOR TREATING MIXTURES 0F OXY SALTS O1 ARSENIC, ANTIHONY, AND rm Illo Drawing.

This invention relates to a process for treating mixtures of alkali stannates, arsenates and antimonates, and more particularly to a process for treating mixtures of alkaline oxy- 5 salts of tin, arsenic and antimony which are formed as a by-product during the refiningof lead.

The invention more specifically relates to the separation and recovery of the tin, arsenic 1 and antimony contained in mixtures of sodium stannate, sodium arsenate and sodium antimonate either as a metal or as salts thereof in a marketable state of purity.

The invention still further relates to the utilization and subsequent recovery of any free caustic alkali, alkali chlorides, alkali carbonates and like substances which may be present in addition to the above mentioned stannates, arsenates and antimonates.

The invention further consists in the new and novel features of operation and the new and original arrangements and combinations of steps in the process hereinafter described and more particularly set forth in the claims. The process, in accordance with the present invention, consists in lixiviating a mixture of the stannates, arsenates and antimonates from which it isdesired to obtain and separate tin, arsenic and antimony with sufiicient hot water to dissolve the stannates and arsenates while leaving the .ant-imonates as an insoluble residue.

The antimonates may be removed from the solution by filtration and utilized as desired. A suitable reagent such as metallic tin, stannous salts, sodium sulphide, or their equivalents, is then added to the solution to precipitate various impurities contained therein such as antimony, tellurium, lead and copper. These impurities, if allowed to remain in the solution, would interfere with subsequent operations.

The solution may be passed through a filter or decanted for removing the above impurities, or should it not be essential ,in any particular instance to obtain substantiall pure antimonates, thisstep may be omitte in which case the impurities such as lead a and copper maybe removed together withthe antunonates by a single filtration.

.paratively insoluble, whereby they will be Application filed January 20, 1927. Serial No. 168,409.

The hot solution of sodium stannates and arsenates may then be electrolyzed using insoluble anodes whereby metallic tin may' be deposited at the cathodes, caustic alkali being liberated and the alkali arsenates remaining in solution.

The arsenates may then be recovered from the spent electrol e by cooling the same to a temperature at w oh the arsenates are'comcaused to crystallize out. The crystals may then be removed by filtration from the caustic mother liquor, which may then be eva orated for the recovery of fused caustic al ali for subsequent use. e

The arsenate may be recovered from the electrolyte, if desired, by treating the same with hydrated lime or milk of lime or an equivalent reagent whereb calcium arsenate is precipitated and the al ali radical is liberated as free caustic alkali. An alkali carbonate present in the solution wil at the same time be converted to caustic alkali.

The calcium arsenate may then be removed from the solution by filtration and the caustic alkali recovered by evaporation. f

Asa more specific example of the rocedure to be followed in carrying out t e invention, the treatment of a mixture of sodium antimonate, arsenate, and stannate resulting from the refining of lead by the Harris process will be described, although the process is not to be limited to these particular steps and substances but only in accordance with the appended claims. v

The composition of such a mixture may vary widely, depending upon the analysis of the impure lead bullion from the refining of ans ysis which it results, but the following w is typical:

. V Pu eeni Arsenic 8.1 Antimony 62' Tim. 9.5 Free caustic soda 9.5 Sodium chloride 8.1 Lead 0,8

In the treatment of such a mixture according to the present invention it is first mixed i of carbon for reduction to marketable metal-.

equipped with steam coils for heating and with a motor-driven agitator. The amount of water used is preferably such as will give a solution containing approximately 45 rams of tin per liter, but this ma .vary with- 1n rather wide limits according to the strength of solution desired. The agitation and heating is continued until substantially all of the sodium arsenate and stannate, and the free caustic soda, sodium chloride and other soluble salts, are dissolved.

Y The resulting pulp is then forced through a suitable filter, such as, for example, a plate and frame filter press, and the solution separated from the insoluble sodium antimonate remaining in suspension. The sodium antimonate may be washed in the press with sufficient water to remove the dissolved salts, the wash water being returned to the above mentioned tank for the lixiviation of a succeeding batch of mixed sodium arsenate, stannate and antimonate.

The washed filter cake of sodium antimonate is dried and smelted with the addition or other suitable reagent, to precipitate lead,

copper, and other deleterious im urities. These recipitated' impurities are t on removed m a second filter press.

- The urification of the solution may, if desired, e carried out before its separation from the sodium antimonate, in which case the sodium antimonate and the precipitated impurities are filtered ofi together. This proce ure is somewhat simpler than performing I the two steps so arately, but does not produce the antimonate m as high a state ofpurit The solution after being purified, as a ove described, and after having the antimonates removed, may be treated for the recovery of tin'by an suitable means such as by electrolysis. t may, for example, be placed in electrolyzing vats and maintained at a suitable temperature such as approximately 90 v centi-grade, at which temperature the reaction is most favorable. -A coating of molten ar aflinmay-be maintained on the surface 0 the electrolyte to prevent eva oration thereof, to 'p'reventthe formation 0 spray and to prevent the caustic from becoming carbonated from the carbon dioxide in the air.

[Suitableelectrodes such as insoluble iro means;

propriate value for efliciently 'electrolyzing tin such as, for example, approximately 10 to 20 am'peres per square foot.

- .By operating an electrolyzing vat under the above conditions, a firm deposit of tin may be obtained on the cathodes, the tin having a marketable state of urity such as 99%. The tin content of the so ution ma by this process, be reduced to a proximate y 1 ram per liter, the presence 0 an excess of so um arsenate not appreciably interfering with the deposition of tin from the sodium stannate.

The sodium combined as'sodium stannate is released by electrolysis as free caustic soda.

After cooling, the crystals are separatedfrom the solution byfiltration in a suitable filter, such as a plate and frame press or a Sweetland 'filter. The crystals of sodium arsenate may then be sold as such or may be used for the production of insecticides such as calcium arsenate. The filtrate may be evaporated fr the removal of water and the production of fused caustic soda which can be re-used for refining a further quantity of lead bullion.

When solutions of sodium arsenate containing sodium stannate are cooled to crystallize out the sodium arsenate the crystals of the latter which are formed always contain a considerable amount of sodium stannate which cannot easily be removed from them, but if tin is largely removed from the solutions by electro-deposition before the sodium arsenate is crystallized, as above specified,

the sodium arsenate crystals obtained contain practically no tin. A

The sodium arsenate solution remaining after the electro-deposition of the tin may be utilized directly for the manufacture of calcium arsenate if it does not contain suacient free caustic to interferewith the precipitation of calcium arsenate. In order to, accomplish this the solution from the electrolytlc tanks is agitated with the necessary amount of hydrated lime or milk of lime to form calcium arsenate with the sodium arsenate present. The resulting calcium arsenate may then be filtered off and washed in a suitable ress. By the reactionbetween the lime an the sodium arsenate free caustic soda is formed simultaneously with calciumv arsenate, so that the final. solution contains the free caustic originally resent, that liberated by the electrolysis o thesodi'um stanj vention have been shown and described and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes in the several steps of the recess and in its operation may be made by t ose skilled in the art without departing from the spirit of the invention. v

What is claimed is:

1. The process for treating mixtures of alkali oxysalts including salts of tin and arsenic in which, the arsenic is present in substantial amounts relative to the tin content, which comprises dissolvin the arsenic and tin salts, heating'the sdlution', electrolyzing the hot'solution to deposit substantially the entire amount of tin contained therein and then crystallizing and removing the salts of arsenic.

2. The process for treating mixtures of alkali oxysalts of tin,arsenic and antimony,

which comprises treatin the mixture with hot .water whereby the a kali o salts of tin and arsenic are dissolved, removing the residue containing insoluble alkali oxysalt of antimony, and removing substantiall the en tire amount of tin from the solution y heating the solution and electrolyzing the same whereby metallic tin is recovered therefrom,

3. The rocess of treating mixtures of alkali oxysa ts of tin, arsenic and antimony in which the arsenic is resent in substantial amounts relative to t e tin content, which comprises treating the mixture with hot water whereby thealkali oxysalts. of tin and arsenic are dlssolved, removing the residue 7 containing insoluble alkali salt of antimony, and electrolyzing the hot solution to deposit substantially the entire mass of tin-contained therein.

In testimony whereof we have hereunto set our hands.

amLvmLE FLETCHER PERKINS. CHAS. W. HANSON. BERRY MARVEL OHABRA. 

